Multicast/broadcast is a service that permits sources to send a single copy of the same data to an address that causes the data to be delivered to multiple recipients. Under multicast/broadcast only one copy of a message passes over any link in a network and copies of the message are made only where paths diverge. From the network perspective, multicast/broadcast dramatically reduces overall bandwidth consumption, since the data is replicated in the network at appropriate points rather than in the end-systems. Further a server, which is sending multicast message needs to manage only one session.
Multicasting in the internetworking between a fixed network, like for example the Internet or any other IP-based backbone network and a mobile network like, General Packet Radio System GPRS or Universal Mobile Telecommunication System UMTS is currently developed, because especially in the wireless network new challenges occur. These challenges are for example the mobility of the end users and low transmission bandwidth of the mobile network on the air interface, but also the lower reliability due to the packet loss on the radio interface compared to the fixed networks.
Multicasting in the internetworking between a fixed network and a mobile network like, General Packet Radio System GPRS or Universal Mobile Communication System UMTS is presented in the following according to the actual multimedia multicast/broadcast MBMS architecture of the General Packet Radio System GPRS network as depicted in FIG. 1.
The GPRS is the packet-switched enhancement of the Global System for Mobile Communication GSM, which is a circuit switched network. In GPRS, the user can be permanently online connected paying only for the real data transfer. In order to fulfill the new requirements some changes are introduced into the GSM, amongst other new logical nodes, the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN). The main functions of the GGSN involve interaction with external IP packet networks providing for example connections to Internet Service Providers ISPs. For the purpose of providing multicast/broadcast service the GGSN can communicate with Broadcast/Multicast Service Centre BM-SC receiving a content from a Content Provider being located either in the mobile network or in the external network, thus the BM-SC entity is responsible for the provision of multicast/broadcast, like for example for bearer establishment and data forwarding. Further possibility for providing multicast/broadcast is by means of a Multicast Broadcast Source, which can be located in the mobile network or in an external network. The SGSN serves all GPRS subscribers that are physically located within the geographical SGSN service area. It forwards incoming IP packets addressed to a mobile station. Additional to the new logical nodes also new interfaces between the nodes are to be defined as it is depicted in FIG. 1.
The similar nodes and interfaces are also used in the next generation of the wireless networks, like the UMTS.
The introduction of multicast/broadcast into wireless network has to deal with problems being relevant for the mobile networks, amongst other with the mobility of the end users and low transmission bandwidth of the mobile network on the air interface.
In particular the mobility of the users has impact on different development directions.
For example due to users movement, different networks are to be constructed to provide service to the customers. Hence, depending on the network co-operation between operators, a possibility is provided to offer the subscribers a coverage area being much wider.
This functionality is called roaming. Roaming might be provided if some administrative and technical constraints are fulfilled. From the administrative point of view, issues like for example charging, subscription agreements must be solved between different operators each offering an operational domain. From the technical point of view some topics are consequence of the administrative matters, such as the transfer of call charges or the transfer of the subscription information between networks. Others are needed simply for roaming to be possible at all, such as the transfer of location data between networks, or the existence of a common access interface.
It should be noted that roaming, in which the user can move and keep access to the service is only possible if some conditions are met. First, the operating domains and their operators must communicate between themselves. For this purpose a number of standardized interfaces is defined, by means of which the so-called Service Layer Agreement SLA might be transferred. Second, the user must have the possibility to access a service in different networks.
In a common praxis, a user has a subscription relationship with a single operating domain, being often called home operating domain, for example, a home PLMN (Public Land Mobile Network). A user usually has access to a service in the home operating domain. The varicosity of the services for accessing depends on the subscription.
Furthermore a distinguishing between a national and international roaming is made, depending whether the operating domains belong to the same or to different countries.
Mobile telecommunications networks, such as GPRS or UMTS, aim to provide services such as voice, data, and multimedia via computing devices over network infrastructures. Particularly, the provision of services being multicasted or broadcasted to the users is an important part of the evolution of these networks. In the following the abbreviation MBMS will be used for the Multicast/Broadcast Multimedia Service.
Currently there are mechanisms for supporting a provision of Multicast/Broadcast services. MBMS services are differentiated in one network using the Temporary Mobile Group Identifier (TMGI). A TMGI uniquely identifies an MBMS bearer, which transports a MBMS service, worldwide. The TMGI is structured in a way that it is possible to define within every network an unique TMGI for a particular service. The TMGI will be described in more details afterwards.
However, if an MBMS UE roams in another MBMS enabled network, the MBMS UE is only able to receive the activated MBMS transmissions, if the visited network supports the service and then the user has to know how to access the service. This means that a visited network in order to provide the home MBMS service to the users visiting it, must also announce MBMS services and sends MBMS notifications for MBMS Services of the foreign networks besides the own service portfolio. Consequently, MBMS roaming is only possible, when potentially all services of all service providers are offered through all mobile networks.
Therefore in order to support roaming, the MBMS functionality is required in all networks. Thus, if a visited mobile network does not support the MBMS feature at all or does not support MBMS roaming, it is not possible to offer MBMS services to users being subscribed to MBMS in the home network and visiting the visited mobile network.
In the current solution, if a network does not offer the MBMS feature at all, then the roaming of the MBMS service does not work when an MBMS UE is roaming into that network. For example, the user might receive for example in a foreign country a MC/BC service in a foreign language, but it is not possible to offer to the user the home MC/BC service in the home language.
Moreover, besides the provision of the technical features, also an agreement on the roaming policy is to be provided. It might be possible that a mobile-network implements MBMS functionality, but the operator does not allow the usage of MBMS for the visiting subscribers, for example to save MBMS recourses for the own users and own services. Consequently, also in this case the roaming solution would not work.